This invention relates to a film feeding circuit for a camera.
Japanese Laid-Open Patent Application No. 121,524/74 discloses a film feeding system for a camera in which a motor is operated to rotate at its full speed to feed a film in response to the termination of a shutter operation while simultaneously perforations formed in the film are electrically detected at a given location to be counted by a counter so that when the count therein reaches a given value, the motor is deenergized, thus feeding the film by one frame. The system suffers from a disadvantage that when a stop instruction is produced as the count reaches a given value, the motor continues to coast to cause a film slip corresponding to a number of perforations, thus degrading the accuracy of stopping the film at a given point. Also, when no film is loaded in the camera to prevent perforations in the film from being detected, the motor, once started at the termination of a shutter operation, continues to be energized, thus disabling an operation of the camera. Furthermore, since a power supply is normally maintained on, there results undesirable, wasteful power dissipation when no film feeding operation takes place. Additionally, there must be provided some means which deenergizes the motor in response to a stop motion of the film while the motor continues to be energized, as occurs when a film feeding operation entirely completed, namely, after the last frame of film has been fed. To cope with this problem, a detecting resistor may be inserted in series circuit with the motor to detect an increase in the motor current which occurs as a result of the stop of the motion after the full length of the film has been fed, thereby terminating the energization of the motor. However, the insertion of the detecting resistor in series with the motor causes a sacrfice in the motor characteristics such as starting torque or speed-torque curve, and may additionally cause an erroneous detection of a high current upon starting the motor or a current flow during a fluctuation in the load, thus causing an erroneous deenergization of the motor. While a control in accordance with the content of a counter may be contemplated, a close control cannot be achieved since a single signal is produced by one perforation.